1. Technical Field
This invention relates generally to optical relay systems, and more particularly to a substrate guided relay that incorporates a polarization rotating apparatus, such as a half-wave plate, configured to transform light having substantially a first polarization to a second polarization within the substrate guided relay.
2. Background Art
Substrate guided relays are devices that transmit light rays from a source to a viewer. Generally speaking, substrate guided relays are optical transfer devices that include a substrate, which may manufactured from glass or fused silica, and which directs light from a relay input to a relay output. This light can be guided along its path by the optical transfer properties of the substrate. Additionally, the optical transfer properties of the substrate can work in tandem with reflective or diffractive devices coupled to the substrate. The surfaces of the substrate can also work to direct the light to its intended destination. In many applications, this end destination is a viewing region that is directed to a projection surface or a user's eye. One application of substrate guided relays is that of a near-to-eye display in which the viewing region projects directly into the pupil of a user.
Substrate guided relays generally include three basic components: an input that collects and receives light from a source, a substrate that transfers the light, and an output that delivers light away from the substrate. In many applications, it is advantageous to keep the various components of the substrate guided relay assembly small, as they are sometimes used as head mounted displays or other compact display systems. This desire to keep size to a minimum creates challenges, however, for the designer. In particular, when a source of light is small, the light often has a smaller spatial extent. It can therefore be challenging for a substrate guided relay designer to create a display having a pupil that is much larger than the extent of the source. Where small light sources are used, such as scanned beam light sources, it is often advantageous to “homogenize” the incoming light by making many copies of the light. By way of example, commonly assigned, co-pending U.S. patent application Ser. No. 12/167,892 entitled “Optical Substrate Guided Relay with Input Homogenizer” filed Jul. 3, 2008, and commonly assigned, co-pending U.S. patent application Ser. No. 12/167,882 entitled “Substrate Guided Relay with Homogenizing Input Relay,” filed Jul. 3, 2008, each of which is incorporated herein by reference, teach methods and apparatuses for homogenizing light with substrate guided relays. While homogenization is a useful technique to improve output image quality, it sometimes requires the use of sophisticated optical coatings. It is sometimes challenging to manufacture well-behaved coatings integrated with substrate guided relays in a cost effective manner. Additionally, some coatings are easier to manufacture than are others.
There is thus a need for an improved substrate guided relay for use in light homogenization applications.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.